Method and apparatus for continuously drawing a glass sheet



March 15, 1960 5. LONG 2,928,212

METHOD AND APPARATUS FOR CONTINUOUSLY DRAWING A GLASS SHEET Filed Jan.18, 1956 4 SheetsSheet 1 FIG. 1

JNYENTOR fiemard 1on9 ATTORNEYS March 15, 1960 B. LONG 2,928,212

METHOD AND APPARATUS FOR CONTINUOUSLY DRAWING A GLASS SHEET Filed Jan.18, 1956 4 Sheets-Sheet 2 INVENTOR ATTORNEYS March 15, 1960' B. LONG2,928,212

METHOD AND APPARATUS FOR CONTINUQUSLY DRAWING A CLASS SHEET Filed Jan.18, 1956 4 Sheets-Sheet INVENTOR Bernard long B. LONG 2,928,212

METHOD AND APPARATUS FOR CONTINUOUSLY DRAWING A GLASS SHEET 4Sheets-Sheet 4 March 15, 1960 Filed Jan. 18, 1956 I N VENTOR Bernardlong ATTURNE Y5 United States atent METHOD AND APPARATUS FORCONTINUOUSLY DRAWING A GLASS SHEET Bernard Long, Paris, France, assignorto Compaguies Reunies des Glaces & Verres Speciaux du Nord de la France,Paris, France, a'corporation of France Application January 18, 1956,Serial No. 559,998

Claims priority, application France January 24, 1955 5 Claims. (Cl.49-'--17) My invention relates to apparatus for the continuous drawingof a glass sheet from a shallow bath, and especially to an apparatusaccording to which the sheet is drawn in a horizontal or nearlyhorizontal direction.

it is well known that glass is ordinarily drawn from a shallow bath in adirection vertical to the surface of the bath, the sheet itself risingfrom a thickened portion at its base, known as its foot, the twoopposing faces of this foot curving gradually away from the plane of thesheet so as to merge into the horizontal surface of the bath.

it is also well known that after travelling at certain vertical distancethe sheet is generally bent into a horizontal position over a bendingroll and that it is then introduced into the annealing lehr while in ahorizontal position.

' This method of forming the sheet by drawing it vertically from thesurface of the bath has certain disadvantages. Among these is the factthat a substantial drawing force is necessarily exerted on the skin ofthe foot of the sheet and of the sheet itself as it is hardening, sincein addition to the internal friction and superficial forces, thisdrawing must overcome the relatively strong pull of gravity on the glasswhich has been lifted from the bath and is positioned between itssurface and the bending roll. s

As a consequence of the fact that this d awing force is strong, the-skin in question is stretched and is there-.

fore elongated while it is hardening.

Under these conditions the irregularities in temperature which affectthis skin result in. unevenesses or waves in the surface known as batterand striae which are even more marked, all other things being equal,when the skin is under the greatest tension. s

In my copending application Serial No. 54,127, filed November 25, 1955,entitled Improvements in the Continuous Drawing of Glass into Sheets,and now abandoned I claimed a process of drawing from a shallow bathwhich, for a given speed of drawing and a given thickness of the sheet,permits a substantial reduction in the magnitude of the unevenesses inits surface, especially by reducing the elongation of the skin of thefoot of the sheet and the skin of the sheet itself during its hardening,but this process delivers sheets, the surfaces of which still leavesomething to be desired.

The principal object of the present invention is to provide an apparatusfor continuously drawing a sheet from a shallow bath which, for a givendrawing speed and a given thickness of the sheet, permits an evengreater reduction in the magnitude of the unevenesses of the surfacethan does the aforementioned process.

Another object of the present invention is to eliminate those defects inthe sheet which result from its bending over a bending roll.

With the apparatus constituting my invention, the following results areachieved:

(1) The drawing force need no longer lift the weight of the foot of thesheet and of the sheet itself up to the bending roll.

( 2) The greater partiof the. thickness of the foot of 2,928,212Patented Mar. 15, 1960 ice I Z the sheet consists of glass having arelatively high viscosity, with the remainder consisting of glass havinga low viscosity.

(3) The sheet itself is very rapidly hardened. v

The process utilizing my invention begins with the formation of a skinon the surface of the draw bath, the viscosity and thickness of whichare rapidly increased as the glass approaches the back end of the tankor draw pot, that is to say, the end from which the glass is drawn.

This end is so constructed that much less viscous glass is interposedbetween it and the skin before the sheet leaves the tank in a horizontalor nearly horizontal direction.

it will immediately be seen that the low viscosity glass which flowsunderneath the relatively stiff skin at the surface of the bath servesto reduce the friction between this skin and the walls of the tank.Moreover, since the sheet leaves the tank in a horizontal or nearlyhorizontal direction, it will be readily understood that the followingtwo important advantages result from the general constructionhereinbefore described:

(1) The drawing force required for a given speed and thickness of thesheetis reduced as much as possible.

(2) This drawing force affects almost the entire thickness of the sheet.j

The process utilizing my invention consists, inthe first place, of thestep of extending the back end of the drawing tank to form a thermalconditioning channel or spout for the foot of the sheet. This spout ishorizontal or nearly so, and is constructed in such a manner that itradiates poorly towards the top and supports the foot of the sheet for aconsiderable distance while'ithe sheet is being drawn in a horizontal ornearly horizontal.direction. The greater part of the thickness of thefoot of the sheet isformed from the highly viscous skin which re sultsfrom a substantial hardening of the surface of the bath, and theremainder of its thickness from warmer glass which has travelled alongthe bottom of the drawing tank, the temperature of which is increased asit passes over the thermal conditioning channel or spout. My processcomprises also on the other hand the step of rapidly stiffening thelower face of the sheet before placing it in a horizontal or nearlyhorizontal position on one or more conveyor rollers preceding a seriesof rollers which form a horizontal or nearly horizontal table designedto assure the overall smoothness of the sheet before it enters theannealing lehr. I

The fundamental characteristic of my process is the production of a verylong thin foot for the sheet which is supported throughout the greaterpart of its length by a thermal conditioning channel or spouthereinafter referred to as a drawing spout. This foot has as high atemperature gradient as possible between its highly vis cou's uppersurface which is in contact with the atmosphere, and its much lessviscous lower face which is in contact with the spout.

This gradient ensures that only a minimum drawing force will be requiredand that very little deformation will result from the bending andflowing of the free part of the foot of the sheet and of the sheetitself between the spout and the first conveyor roller. The gradientre-. sults from certain special arrangements. In the first place, thefollowing points should be mentioned:

(1) The warmer glass whichflows along the bottom of the tanker draw potis led to the. spout by progressively decreasing the depth of the tankfrom its front end to the entrance of the spout.

; if thedrawing spout were notmade of a refractory may terial having alow overall emissivity in the range of temperatures between about 1000"C. and about 1100 C. This material may consist, for instance, of puremagnesia, alumina or silica, free from traces of iron, or even thosesilico-aluminous refractories manufactured from raw materials whichcontain only minimal quantities or highly absorbent impurities such asiron oxides.

The temperature gradient within a layer of glass lying, like the foot ofthe sheet in my process, on a very hot hearth made of a refractorymaterial, is largely influenced by the emissivity of this hearth, anemissivity which is, in general, greater than that of the glass.

It would be absolutely hopeless to try to increase the temperaturegradientrin the layer of glass which rests on the drawing spout byheating the spout if it were made of an ordinary refractory materialwhich, by reason of its own strong radiation, could not fail tosubstantially heat the upper part of the layer of glass.

4. only from its surface but also from its sub-adjacent layers. Such anexchange of heat would cause a reduction in the temperature gradientwhich gradient results from the convective cooling which is the basis ofthe substantial hardening previously mentioned.

The presence of the screen renders the loss of heat by radiationupwardly from the foot of the sheet negligible and consequently permitsthe temperature gradient through the sheet to be brought to a maximumvalue by means of vigorous convective action at its surface.

The screen in question may consist of a vault which reflects back alarge portion of the energy radiated by the foot of the sheet and may bemade, for example, of

* which may be of any type, provided it will not harm the In order thatthis concept may be clearly understood,

it should be remembered that the overall emissivity of magnesia, aluminaand silica, when free from ferruginous impurities, in the temperaturerange between about 1000 C. and about 1100 C., lies between 0.3 and 0.5,whereas that of the silico-alumino'us materials ordinarily used in theconstruction of drawing tanks is greater than 0.7, running sometimes ashigh as 0.8 and sometimes 0.9.

The process utilizing my invention can thus be carried out only with adrawing spout which is, in the first place, long enough to permit a filmof glass which glides over it to be sufficiently heated by conduction,and, in the second place, provided with walls which, where they contactthe glass, have a low emissivity in the temperature range between 1000C. and 1100 C.

An emissivity of 0.5 may be considered to be the upper limit when aclear glass having an iron oxide content (expressed as Fe O no greaterthan 0.10% is being drawn. If, however, the glass being drawn is morehighly absorbent by reason of a higher percentage of iron o'xides orbecause of the presence of other highly absorbent constituents, theupper limit of this overall emissivity for the spout may be raised to0.7.

When the lower surface of the draw po't, which is made of a materialhaving a low overall emissivity, is heated (by meansof electricalresistances, flames, or the like) the glass which is in contact with itsupper surface is given the low viscosity required by my process withoutmaterially reducing the high viscosity of the greater portion of thethickness of the foot of the sheet. But the requirement that the drawingspout radiate poorly in an upward direction may be even more strictlysatisfied by lining its upper surface with a sheet of metal which doesnot oxidize readily and which is highly resistant to corrosion by theglass, such as platinum and certain of its alloys. This arrangementreduces the overall emissivity below 0.2, and also possesses theadvantage of permitting the spout to be made of ordinary refractorymaterials.

Since the metal lining may be easily heated electrically by the Jouleeffect, it will readily be seen that the use of a spout having ametallic lining permits the glass forming the lower part of the foot ofthe sheet to be rendered highly fluid while the heating of its upperportion is held to a minimum, thus creating a particularly hightemperature gradient between its ripper and lower surfaces. Thisgradient generally exceeds 80 C. per centimeter.

This gradient may be further increased by placing a screen over the footof the sheet which has the property of reflecting back a large portionof the energy which the said foot radiates upwardly.

Since the process utilizing my invention comprises the substantialhardening of the skin of the foot of the sheet, it will be appreciatedthat in the absence of this screen the foot of the sheet would exchangeheat with the atmosphere and ambiant objects by radiation not platinumwhere the metal is in contact with it. The sheet of platinum acts bymeans of its own high reflecting power.

Thus, as has already been pointed out, the drawing spout increases thelength of the draw pot and must necessarily have a certain length, sincethe increase in the temperature of the film of glass along the bottom ofthe lower part of the foot of the sheet which is necessary in order tocarry out the process utilizing my invention takes a certain amount oftime.

This spout may be made an integral part of the draw pot, but for severalreasons, especially its length, the facility of replacing it, and itsparticular construction, it is desirable to make it in the form of aseparate piece which is positioned against the end of a pot having arelatively simple shape and made of an ordinary refractory material.

The drawing spout is, in general, horizontal, but it may be advantageousto incline it slightly away from the horizontal, especially in order tofacilitate the delivery of the sheet.

The bottom of the spout may be flat, but, to facilitate the productionof a sheet having a constant thickness throughout its width (with theexception of the edges), this bottom is slightly concave at its centerso that the sheet of glass which covers it is slightly thicker therethan in the vicinity of its edges.

When the foot of the sheet leaves the spout, its lower face isvigorously cooled, preferably by convection, by means of a homogeneoussheet of air which sweeps along it, in order that the sheet itself maycome in contact with the first conveyor roller a short distance beyondthe spout without any injurious effect on the polish of its surface.

Thus, the process utilizing my invention possesses over known processesin which the glass is first drawn vertically and then bent, theimportant advantage that the lower face of the sheet is not affected byimperfections in the surfaces of a bending roll.

If at the same time one or both faces are cooled by means of watercoolers which still further increase the viscosity of the thick skinwhich has already been formed, the rigidity of the sheet will be sogreat that any longitudinal sagging due to bending and flowing betweenthe spout and the first conveyor roller will be slight.

In the vicinity of the spout the two edges of the unsupported or freeportion of the foot of the sheet are stiffened and supported by twopairs of small roller wheels of a known type. Additional pairs of smallroller wheels may be positioned between these first rollers and theconveyor roller in order to support the edges of the sheet and therebyreduce the longitudinal and transverse sagging of the sheet as much aspossible.

The conveyor roller corrects almost all of the transverse sagging. Thelongitudinal sagging and the residue transverse sagging are corrected bythe series of rollers which follow the conveyor roller and form a tableover lehr. 1

In order that the invention may be more clearly understood, severalembodiments of my invention will now be described, purely by way ofexample and without in any way limiting the scope of the inventionto thespecific apparatus shown in the attached drawings; in which:

Figure 1 is a vertical longitudinal cross-section showing the assemblyof a drawing machine which comprises a shallow tank or pot provided witha long thermal conditioning spout, the bottom of which is heated andcarries the foot of the sheet, the cooling devices which form the skinof high viscosity in the foot of the sheet,

and the members which supportthe sheet until it enters the annealinglehr;

Figure 2 is avertical longitudinal cross-section, 'on a larger scale,showing the portion of the foot of the sheet which lies on the spout,the free portion of this foot,

then the sheet itself between the second set of small roller wheels andthe conveyor roller, and finally the means for stiffening the sheetbefore it comes in contact with this roller;

Figure 3 is a simplified vertical longitudinal crosssection showing adevice for drawing the sheet in an approximately horizontal directionfrom a slightly inclined spout;

Figure 4 is a vertical cross-section taken in a plane transverse to thedrawing direction and showing a spout showing a separate spout and thefree end of the foot of the sheet, each of the edges of which is cooledand sup? ported by a pair of small roller wheels; I

Figure 7 is a partial vertical elevation taken from the side nearest theannealing lehr showing the left-hand half of a separate spout having aheated platinum lining; and

Figures 8 and 9 are transverse vertical cross-sections showing twoembodiments of a separate spout having a bottom which is slightlyconcave at its center.

As shown in Figures 1 and 2, the" stream of glass 1 which arrives at thethermal conditioning zone of a tank furnace travels from left to right,in the direction of the arrow, into the drawing tank or pot 2 andcontinuously replenishes the draw bath 3, the surface 4 of which iscovered by the movable screen '5 made of arefractory material;

The drawing tank or chamber itself is elongated at the end opposite thepoint at which the glass enters, so as to form a fairly long thermalconditioning spout 6, which is the basic element necessary to carry outthe process constituting my invention and which is also called thedrawing spout.

The bottom 7 of the tank or chamber 2 rises progressively from theentrance 2a forthe glass to the drawing spout so as to direct into assmooth a path as possible the current of warmer glass which flows nearthe bottom The blowing tube 15 is pierced along its lower righthand sideby a number of holes which are arranged in several rows and so spaced asto produce a substantially homogeneous sheet of air at a short distancefrom the surface of the tube. Y

i, This sheet ofair is directed over the surface of the glass bath andsweeps along this surface as indicated by the arrows 16. It is thendrawn in by the suction tube 17 which is provided with, a number ofholes distributed in severalrowsalong its lower left-hand side.

The tubes 15 and 17 which extend all the way across the bath 3 are madeof stainless steel. In order to protect them against overheating, eachtube rests freely on a small tube support through which water circulatesand which is designated'by the same number as the tube, accompanied by aprime mark The convective cooling of the surface of the bath which isaccomplished by the cooperating blower and suction tubes 15 and 17brings about a steep temperature gradient in the superficial layers. Thesurface of'the bath becomes covered. with a very stifi 'skin'which restson relatively mobile subjacent glass.

The layer of glass 18 which covers the spout and constitutes the longestpart of the foot of the sheet is quite thin. It consists, at the top, ofthe skin formed by convective stiffening of the surface of. the bathand, at the bottom, of only a thin film of warmer glass which hastravelled in the line indicated by the arrows 8 along the bottom 7 ofthe tank 2.

- The temperature gradient thus created would be scarcely suflicient tocarry out the process utilizing my invention if other supplementarymeasures were not employed. In

other words, the foot of the sheet must, while on the spout, besubjected to a special thermal conditioning, which is accomplished asfollows:

(1) The blower tube 19 in cooperationwith the suction tube 20 vigorouslycools the upper part of the foot of the sheet by convection, the aircirculating from the first-named tube to the second as shown by thearrows 21.

(2) The drawing spout is heated by the electrical resistance 14'. If itis necessary to vary the heating of the spout transversely, theelectrical resistance 14 is divided into several sections which areseparately fed, or it may be suflicient to rely on the spacing of itscoils, placing them close together where the most heat is required andspa;- ing them further apart where less heat is needed.

' (3) The drawing spout (and consequently the pot in the case ofFigure 1) is made of a material such as pure alumina or pure magnesia,free from traces of iron, and I thus having, as is well known, anoverall emissivity less than,0.5 for temperatures of the order of 1100C., to l which the upper faceof'the draw spout is subjected.

Since the construction from pure alumina or magnesia of a one-piece pothaving a spout is a diificultmatter,

and the fact that a film having a relatively high mobility is formed atits bottom by heating the sole of the spout .by means of the electricalresistance 14 cooperate to establish a steep temperature gradient whichinsures, on the one hand, very little deformation of the foot of thesheet and the sheet itself due to bending and flowing, and, on the otherhand, only a minimum of friction between the foot of the sheet and thespout.

:If necessary, the efficacy of the two above-described arrangements maybe still further increased by the choice of a suitable material for thelower surface of the vault lintel 22 which extends over the uppersurface of the foot of the sheet, the extrados 22a of this lintel beingheat insulated.

" By constructing this vault lintel with especially absorbent refractorymaterials due, for example, to a high percentage of iron oxides, it isassured that the vault will act as a radiation reflecting meansandreturn to the foot of the sheet the greater part of the energy radiatedby the sheet to the vault. The conditions which are, as has already beenexplained, most favorable to an increase in the temperature gradientwithin the sheet, are thus brought about.

Bricks of magnesia or chrome-magnesia containing more than of ironoxides constitute suitable highly absorbent refractories.

In connection with the description of Figure 4, another solution oftheproblem of the reflecting screen above the foot of the sheet isdisclosed.

On leaving the spout, the edges of the free part of the foot of thesheet 18a (see Figure 2) are supported by two pairs of small rollerwheels 23. It must be emphasized that this free part of the foot of thesheet is stretched only slightly since the greater part of its thicknesshas already been considerably stiffened. The true sheet having parallelsurfaces thus begins at a relatively short distance from the spout.

However, this sheet has a tendency to droop after it leaves the spoutand it is advisable to hold it as taut as possible between the two pairsof small roller wheels 24 before it reaches the conveyor roller 25 andthe subsequent series of rollers 26 (Figure 1) the uppermost portions ofwhich form a table on which the sheet acquires the desired smoothness.

The film of relatively low viscosity which is formed by contact with theheated spout is rapidly hardened by means of the sheet of air emanatingfrom the blower tube 27 (Figure 2). This air is drawn up through thesuction tube 28.

Above the sheet, the water cooler 29 serves to still further increasethe rigidity of the sheet so that the contact of the lower face of thesheet with the conveyor roller 25 does not affect the polish of thisface.

In order to avoid any irregular convective effect on the upper surfaceof the sheet by the air which has been cooled by contact with the cooler29, which might give riseto a little batter, a light current of air iscirculated between the cooler 29 and the sheet by means of the blower 30and the suction tube 31.

A water cooler 32 may also be utilized to cool the conveyor roller 25.

The rollers 26, which form the table which smooths the sheet before itis annealed, are heated slightly by the electrical resistances 33positioned beneath them.

Figure 2 shows more clearly the foot of the sheet 13 which rests on thesole of the spout 6 which is heated by the electrical resistance 14.

The side of the spout is designated by reference numeral 35.

The upper surface of the foot of the sheet is slightly inclined to thehorizontal as a consequence of the drawing, but is not greatlyattenuated, so that the sheet itself attains practically its finalthickness at a short distance from the spout. Its lower face may bebrought into contact with the conveyor roller 25 without any risk ofdamaging the quality of its polish.

On Figure 3, the pot is provided with a spout which inclines slightlydownward. This arrangement takes advantage of the slight effect ofgravity on the free part of the foot of the sheet. The drawing takesplace at a slight angle to the horizontal and then the sheet, afterbeing substantially hardened, is brought into a horizontal position. itis then smoothed on the rollers of the table 26, as in the caseillustrated in Figure 1.

In Figure 4, the spout is, like the pot itself, made of an ordinarysilico-alurninous material.

The upper surface or sole 36 of the spout 6 and its sides are,throughout the length of the spout, covered by a sheet of platinum 37(see Figure 4).

Each end of this sheet is gripped between two small bars 38 made of ametal which is a good conductor, the means for holding these two barstogether being so disposed as to also grip the ferrule at the end of theconnecting cable 39.

The vault lintel above the spout is supported by two angle irons 443;the space between the sides of the spout and the summers of the vault isfilled in with supporting bricks 41 and 42 which rest on the angle irons43 (Figure 4).

The vault is characterized by the fact that its lower surface 22 islined with a sheet of platinum 44 which carries the rings 45, and issuspended by means of the rods 46, the ends of which are hooked andengage in the rings 45.

This sheet of platinum constitutes a screen which refiects the radiationemitted upwardly by the foot of the sheet 18 which rests on the platinumresistance sheet 37 which is electrically heated by the Joule effect.

Since the resistance sheet is brought to a high temperature, forexample, between 1000 C. and l C., the lower face of the foot of theglass sheet 18 is given a relatively low viscosity even though thegreater part of the thickness of the sheet, from the upper surface down,has a high viscosity.

The lateral edges of the foot of the sheet 18 are, like its lower face,rendered relatively mobile by the electrical heating of the resistance37 and it will readily be appreciated that the sliding of the sheet overthe spout requires a very small drawing force.

The foot of the sheet 13 may be compared to a plate of hardened glasswhich is lubricated on the three faces exposed to substantial friction.

in Figure 5, the pot itself is separate from the drawing spout 6, whichis positioned against it in such a manner that its sole, which supportsthe foot of the sheet 18, is level with the edge of the inner surface 7.

The drawing spout 6' is supported through two feet 47, 43 by therefractory brick 13' which is provided with a notch in which the foot 48is seated and a groove in which the heating coil 14 rests.

The drawing spout 6' is made of a material having a low overallemissivity such as pure alumina, magnesia or silica free from traces ofiron oxides.

A separate drawing spout offers the advantage that it may be easilyreplaced in case of wear.

Figure 6 shows how the foot of the sheet 18 is supported by the spoutand how the free part of the foot of the sheet is gripped at its edgesby the two pairs of small roller wheels 23. The chamber beneath the soleof the spout which is heated by the electrical resistance 14 is closedat its lateral ends by two insulating bricks 49 which have been omittedfrom Figure 6 for the sake of clarity but which are shown on Figure 7.

The separate drawing spout shown on Figure] is provided with a platinumlining 37 which is bent back over the lateral sides 35' and foot 47 ofthe drawing spout, thereby forming a rim about the outlet of the spout.

A like rim is provided where the spout engages the pot itself since itis also desirable to provide a platinum lining at this point. Thus,while the foot of the sheet is heated on three surfaces by the platinumlining, it leaves the spout without having come in contact with anythingother than platinum.

Alloys of platinum may be substituted for platinum. In this event, itmay be advantageous, in order to prolong the life of the lining, to makeuse of alloys which the glass does not wet or which it wets only withdifliculty, for example, those containing a certain percentage ofprecious metals such as ruthenium, gold, etc.

The spout of Figure 8 is provided with a sole 50 in contact with theglass which is slightly inclined from the edges towards the center sothat the sheet 18 which rests on this sole increases slightly inthickness from its edges to its center.

This transverse cross-section for the sole facilitates the production of.a sheet which is uniform in thickness throughout its width since thecentral zone has a tendency 1. Apparatus for drawing glass into sheetscomprising a drawing chamber having inlet and outlet ends, the bottom ofsaid chamber sloping gradually upward from the former to the latter, andmerging into an elongated spout at the outlet end of said chamber, bothsaid chamher bottom and spout being made of a material having anemissivity less than .5 for temperatures between 1000 C. and 1100 C. andsaid spout being adapted to admit a stream of glass slightly deeper thanthe thickness of the sheet to be drawn, means for heating the lowersurface of the glass conductively through said spout, convective coolingmeans above said spout for providing a flow of cooling gas in contactwith the upper surface of said glass throughout substantially the entirelength and breadth of the spout, and radiation reflecting means abovesaid spout for reflecting back heat radiated by said glass, saidradiation reflecting means comprising a heat insulating materialsurfaced with a refractory having an emissive power which is not lessthan the emissive power of a chrome-magnesia refractory containing atleast of iron oxides.

2. Apparatus as claimed in claim'l in which the refractory materialcomposing said spout is chosen from the group consisting of silica,magnesia and alumina,

and is substantially free from iron oxides.

883,286 Buchner Mar. 31, 1908 1,328,380 Laird Jan. 20, 1920 1,394,809Colburn Oct. 25, 1921 1,447,702 Whittemore Mar. 6, 1923 1,489,823Crowley Apr. 8, 1924 1,953,023 Mulholland Mar. 27, 1934 2,042,852 Koupal1 June 2, 1936 2,043,029 Blau et' al. June 2, 1936 2,220,433 WellechNov. 5, 1940 2,383,168 Slayter Aug. 21, 1945 2,607,268 Drake Aug. 19,1952 2,744,021 Bargezi May 1, 1956 FOREIGN PATENTS 1898/31 AustraliaMar. 17, 1932 3. Apparatus as claimed in claim 1 in which said lastmentioned refractory is selected from the group consisting of magnesiaand chrome-magnesia containing more than 5% of iron oxides.

4. Apparatus as claimed in claim 1 in which electrical resistanceheating means are provided below the upper surface of said spout.

5. Apparatus as claimed in claim 1 comprising means for cooling thelower surface of the glass as it passes beyond the spout.

References Cited in the file of this patent UNITED STATES PATENTS

